Rechargeable batteries are used in a variety of industrial, commercial and military applications such as fork lifts, uninterruptible power supplies, electric vehicles and military weapons systems.
Rechargeable lead-acid batteries are a useful power source for starter motors for internal combustion engines. However, their low energy density (about 30 wh/kg) and their inability to perform at high temperature, makes them an impractical power source for electric vehicles (EV), hybrid electric vehicles (HEV) and other systems requiring a high energy density power source. Electric vehicles using lead-acid batteries have a short range before requiring recharge, require about 6 to 12 hours to recharge and contain toxic materials. In addition, electric vehicles using lead-acid batteries have sluggish acceleration, poor tolerance to deep discharge, and a battery lifetime of only about 20,000 miles.
Nickel-metal hydride batteries (“Ni-MH batteries”) are far superior to lead-acid batteries, and Ni-MH batteries are currently used in electric vehicles, hybrid vehicles and other forms of vehicular propulsion. For example, Ni-MH batteries, such as those described in U.S. Pat. No. 5,277,999, the disclosure of which is hereby incorporated herein by reference, have a much higher energy density than lead-acid batteries, can power an electric vehicle over 250 miles before requiring recharge, can be recharged in 30 minutes, and contain no toxic materials.
Extensive research has been conducted in the past into improving the electrochemical aspects of the power and charge capacity of Ni-MH batteries, which is discussed in detail in U.S. Pat. Nos. 5,096,667, 5,104,617, 5,238,756 and 5,277,999, the contents of which are all hereby incorporated herein by reference.
The mechanical and thermal aspects of the performance of Ni-MH batteries have important aspects of operation. For example, in electric vehicles and in hybrid vehicles, the weight of the batteries is a significant factor. For this reason, reducing the weight of individual batteries is a significant consideration in designing batteries for electric and hybrid vehicles. Battery weight should be reduced while still affording the necessary mechanical requirements of the battery (i.e. ease of transport, ruggedness, structural integrity, etc.).
Electric vehicle and hybrid vehicle applications include a critical requirement for thermal management. Individual electrochemical cells are placed together in close proximity and many cells are electrically coupled together. Therefore, since there is an inherent tendency to generate significant heat during charge and discharge, a workable battery design for electric and hybrid vehicles is judged by whether or not the generated heat is sufficiently controlled. Sources of heat are primarily twofold. First, ambient heat due to the operation of the vehicle in hot climates; second, resistive or I2R heating known as and hereinafter referred to as “joule heating” on charge and discharge, where I represents the current flowing into or out of the battery and R is the resistance of the battery.
Batteries have been developed which reduce the overall weight thereof and incorporate the necessary thermal management needed for successful operation in electric and hybrid vehicles and other applications, without reducing its energy storage capacity or power output. One such battery design is a monoblock battery. Monoblocks are multicavity packaging embodiments in which the cavities are all contained within one enclosure. An example of a monoblock battery is provided in U.S. Pat. No. 6,255,051 issued to Corrigan et al. on Jul. 3, 2001, the contents of which are hereby incorporated herein by reference. Another example of a monoblock battery is provided in U.S. Pat. No. 6,689,510 issued to Gow et al. on Feb. 10, 2004, the contents of which are hereby incorporated herein by reference. Another example of a monoblock battery is provided in U.S. patent application Ser. No. 09/861,914, now U.S. Pat. No. 7,264,901 issued to Gow et al. on Sep. 4, 2007, the disclosure of which is hereby incorporated herein by reference.
Polymers are widely used as materials of choice in prismatic battery enclosures due to advantages including lower cost, lower weight and easier manufacturability when compared to metal enclosures. In order to ensure that such a battery fulfills life expectations it is important to transfer heat away from the battery. Although polymers typically have excellent volume resistivity and dielectric properties, poor thermal conductivity is a drawback. Currently, there exists a need in the art for battery case having a design that may be easily modified for a plurality of applications and provide effective thermal management and mechanical stability. The present invention overcomes deficiencies in the prior art by incorporating a versatile monoblock design with polymer materials having differing thermal resistivity to provide a battery having improved structural integrity, simplified assembly, maximized power volume and low internal resistance.
Known in the art are large format versions of energy storage electro-chemistries such as lead-acid and Nickel-cadmium, multi-cavity packaging embodiments enclosing more than one electrochemical energy storage cell. A number of technical problems had to be solved in order to incorporate these chemistries into a monoblock construction. These problems include, but are not limited to cell insertion, cell stack compression, cell gas and liquid pressure containment, venting, cell electrolyte filling, cell interconnects to external terminals, intraconnects between cells, case sealing and hermeticity, structural integrity of the case, anchoring of internal components against shock, vibration, charging/discharging and temperature cycling.
Solutions to the above problems have been developed that are optimized for electro-chemistries such as lead-acid and Nickel-cadmium. However, due to the differences between lead acid batteries and lithium ion batteries difficulties exist in creating a monoblock battery for lithium ion chemistries. Accordingly, the solutions for lead-acid and Nickel-cadmium monoblock batteries, are not always applicable with respect to creating monoblock lithium ion batteries.
Lithium ion based batteries face the same but more extreme problems than other battery chemistries in addition to facing unique challenges of it's own. These challenges include the need for: extremely low internal resistance; safety related to overheating, over pressurization, and combustion; space for integration of Battery Management Systems (BMS); containment and restraint of gas pressures; case hermeticity to prevent outward or inward flow of water, and degradation of electrolyte.
These challenges have curtailed the ability to realize a large format, multi-cell lithium ion monoblock battery. There is a need for a large-scale lithium ion battery in a monoblock case overcoming the difficulties cited above. Such a battery would have multiple cells in a monoblock case. It is desired that such a monoblock would be able to withstand forces generated by swelling of cell layers. It is also of interest to provide a means of compressing cell stacks. Furthermore, there is a need for monoblock case that is impermeable to the transmission of water. There is also a need for a pressure and liquid/gas management system in a lithium ion monoblock.
The present invention overcomes deficiencies in the prior art by providing solutions to problems cited above.